Transversal Issues in Real-Time Sense-and-Respond Systems Ahmad T. Al-Hammouri Vincenzo Liberatore Huthaifa A. Al-Omari Case Western Reserve University Stephen M. Phillips Arizona State University Support by: NASA: NAG3-2578, NAG3-2799, NNC05CB20C, NNC04AA12A; NSF: CCR ; Department of Commerce: TOP

6/5/2005Ahmad Al-Hammouri EESR '05 2 Real-Time S&R Objective Tele-epistemological vision Networked S&R extend human reach beyond spatial barriers Remote control of physical environment by sense and respond Potential Applications: Industrial automation Automatic asset mgmt. (RFID) Disaster Recovery UAVs [LNK03] Home robotics

6/5/2005Ahmad Al-Hammouri EESR '05 3 Our contributions Formulate Real-Time S&R for Networks research Middleware demonstration Playback buffers Congestion control Work in-progress Multihoming, implementation, etc.

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6/5/2005Ahmad Al-Hammouri EESR '05 5 Real-Time S&R and Networks Real-Time S&R involve the physical environments Real-Time objectives and constraints Real-time objectives: Correctness, reliability, and safety Flexibility, scalability, and efficiency Communication networks No timeliness or QoS guarantees: BW limitation, losses, delays, and jitter Focus has been on: Control theory, real-time systems, middleware, and data bases

6/5/2005Ahmad Al-Hammouri EESR '05 6 Main thesis Networks research is critical for Real-Time S&R Playback buffers Congestion control Quality-of-Service Major technology gap Multimedia streaming, anyone?

6/5/2005Ahmad Al-Hammouri EESR '05 7 Transversal issues S&R control environments: Radically differ in complexity and in applications Include hierarchical levels of abstraction Transversal issues Address the necessity of providing QoS for S&R These are: Adaptability and tolerance Congestion control Security, fault tolerance, etc.

6/5/2005Ahmad Al-Hammouri EESR '05 8 Transversal issues We are currently involved Case: Adaptability and tolerance Congestion control

6/5/2005Ahmad Al-Hammouri EESR '05 9 Adaptability and tolerance S&R systems must be adaptable to Delays Jitter R S d2d2 d1d1 d3d3 didi

6/5/2005Ahmad Al-Hammouri EESR '05 10 Adaptability and tolerance (cont.). d i ’s vary randomly Decompose d i as d i = τ + ξ i. τ : the nominal round-trip delay (predictable across i ). ξ i : the variation (jitter) in every round-trip time delay Two subproblems: Predictable delays Jitter

6/5/2005Ahmad Al-Hammouri EESR '05 11 Adaptability and tolerance (cont.) Predictable delays ( ξ i = 0, d i = τ ) Methods to mitigate predictable delays Sacrificing performance to preserve stability, e.g., robots teleoperation Use of system models: predict a future state Jitter Jitter causes inaccurate predictions in delay- compensation techniques Playback buffers can eliminate jitter

6/5/2005Ahmad Al-Hammouri EESR '05 12 Network delay Packet arrival Playback buffers Sequence number Packet generation Buffer Playback T ime Adapted from: Peterson & Davie

6/5/2005Ahmad Al-Hammouri EESR '05 13 Playback buffers: multimedia vs. S&R Different performance metrics Round-trip delay jitter Playback delays are determined by controller Controller is away from the host that applies the signal Controller needs RTT to detect a delay spike VoIP stream

6/5/2005Ahmad Al-Hammouri EESR '05 14 Our contribution Combined strategies of playback, control laws, and adaptive sampling Controller determines playback delay based on RTT samples Adaptive playback delay Based on the playback delay, Controller determines control signal, and sampling rate

6/5/2005Ahmad Al-Hammouri EESR '05 15 Transversal issues We are currently involved Case: Adaptability and tolerance Congestion control

6/5/2005Ahmad Al-Hammouri EESR '05 16 Congestion control Match sources’ transmission rates to network capacity Achieve fair bandwidth allocation between different flows Example S1: { r 1, r 2, r 3 } = { 0.5, 1.5, 0.5 } S2: { r 1, r 2, r 3 } = { 0.25, 1.75, 0.75 } S3: { r 1, r 2, r 3 } = { 0.0, 2.0, 1.0 } r1r1 r2r2 r3r3 C 1 = 2C 2 = 1

6/5/2005Ahmad Al-Hammouri EESR '05 17 Congestion control (cont.) Define a Utility function, U i (r i ) Performance of system i transmitting at rate r i Mathematical formulation max Σ U(r i ) s.t. Σ r i ≤ C l, l = 1,…, L and r i ≥ r min,i

6/5/2005Ahmad Al-Hammouri EESR '05 18 Congestion control (cont.) Source Sink queue n

6/5/2005Ahmad Al-Hammouri EESR '05 19 Our contribution Choice of a utility function, U i (A i, r i ) Function of speed of physical dynamics, A i Monotonically increasing and strictly concave with r i Tailoring the general optimization framework for S&R r U(A,r)

6/5/2005Ahmad Al-Hammouri EESR '05 20 Additional directions Implement these methods Middleware vs. lower-level layers Exploit transport layer protocols SCTP: Multihoming and reliability to S&R Power management control

6/5/2005Ahmad Al-Hammouri EESR '05 21 Thank you Comments Questions